<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 200px;
            height: 200px;
            background-color: aqua;
            position: absolute;
            z-index: 99;
        }
        .box1{
            width: 200px;
            height: 200px;
            background-color: yellow;
            position: absolute;
           /* 默认情况后来的盒子在上 */
           /* z-index值越大越靠上 默认值是0 */
           /* z-index必须配合定位使用 */
        }
    </style>
</head>
<body>
    <div class="box">1</div>
    <div class="box1">2</div>
</body>
</html>